Additive manufacturing methods, in which an object is built up by binding portions of a construction material together to form the object, are widely considered as providing an important and advantageous alternative to traditional subtractive manufacturing methods, in which an object is formed by removing portions of material to define the surface of the object.
In many varieties of additive manufacturing, a construction material is deposited into a build region as a series of layers, portions of each layer being bound together and being also bound together with previously-bound portions of the layer below, in order to build up an object to be manufactured. One particular class of additive manufacturing, often termed 3D printing, involves the deposition of sequential layers of granular material into a build region, and the selective joining of portions of the layers together, either after or during the deposition of each layer, by the selective application of a liquid binder from, for example, an ink-jet head arranged to travel across the deposited layer and arranged to selectively deposit binder at desired locations on each deposited layer.
Where the engineering requirements for the object to be manufactured do not mandate a high degree of strength in the object, it may be sufficient to consider the manufacturing of the object as having been finished after the process of depositing the binder into sequential layers of granular construction material is complete. Such manufactured objects obtain their mechanical engineering properties principally from the binding strength between the particles of the granular construction material resulting from the presence of the binder. However, relying on the binder to adhere the particles one to another generally results in a low strength and a consequent tendency of the object to easily fracture.
Accordingly, one class of 3D printing technologies uses a granular construction material, such as a metal or non-metal powder, which is subsequently sintered under suitable conditions such as the application of increased temperature or pressure. Especially, objects made from metal powders as the granular construction material can be sintered, for example by heating to a temperature below the melting point of the metal, to achieve an object with substantially improved mechanical properties.
However, when sintering objects made from a granular construction material which, prior to the sintering, includes binder binding the granules of the granular construction material one to another to form the object, the presence of binder coating the granules can interfere with the sintering process and can lead to a subsequent reduction in advantageous mechanical properties, such as hardness and compressive and tensile strength, as compared with parts formed by sintering an equivalent pure granular construction material which does not include any binder.
Accordingly, there exists a need to provide methods and apparatus which are capable of improving the mechanical properties of objects manufactured by such techniques.